Matt Strickland (left) and Bob Lee, members of an ODFW survey crew, capture and mark a large Chinook salmon as part of a population study on the Oregon coast.

CORVALLIS, Ore. – How many Chinook salmon make their way back to the Siuslaw River in the fall?

That is a question important not only to anglers on Oregon’s north coast but also for fisheries as far away as British Columbia and Alaska.

You might say the Siuslaw is an international river because Chinook that originate in its waters will venture as far north as Alaska, supporting recreational fisheries all along the coasts of northern Oregon, Washington, British Columbia and Alaska.

This fall, fishery biologists from the Oregon Department of Fish and Wildlife will capture adult Chinook in the Siuslaw River near Mapleton as part of a broader study to accurately estimate this year’s return. Nets will be placed in the Siuslaw from late August into October to capture the salmon as they travel upstream to spawn. Nets will be monitored while they are in the river so that when fish enter them they can be removed and released as quickly as possible after they are marked by punching a hole in their cheek plates.

The population study is being funded by a grant from the Pacific Salmon Commission, a 16-person body with representatives from the United States and Canada. The commission divides salmon harvests so that each country reaps the benefits of its investment in salmon production and conservation. Studies such as this year’s project on the Siuslaw are used in the management of local and international fisheries.

Under Pacific Salmon Treaty management, Siuslaw fall Chinook are considered an indicator stock. They are one of a suite of populations considered each year when managers get together to set harvest guidelines for the ocean and inland waterways along the north Pacific coast.

The nets will be set at night to take advantage of lower temperatures, according to Shelly Miller, ODFW fish biologist in charge of the project.

“Putting the nets out at night reduces stress on the fish, and reduces interaction with anglers in this popular fishery,” she said.

Once salmon migration into the river has passed its peak, sometime in mid to late October, activities will shift to counting live spawning Chinook and finding and examining salmon carcasses on their spawning grounds. Throughout the season, crews will survey more than 100 miles of Chinook spawning habitat. This information, coupled with angler creel surveys, will give Miller and her crew the information they need to make good estimates of total fall Chinook abundance.

The last time this kind of data was gathered on the Siuslaw was eight years ago. Similar data was gathered more recently for Oregon’s two other coastal indicator salmon populations in the Nehalem and Siletz rivers.

Miller said the data collected from this year’s study will be used to test the less intensive and more cost-effective methods developed eight years ago and inform fall Chinook population estimates in the Siuslaw for several years to come.

Since 2007, population estimates for Siuslaw fall Chinook have ranged from a low in 2007 of 7,000 to a high in 2011 of 31,000 fish. During that same time period, estimates for the other two indicator salmon populations have ranged from 4,000 to 17,000 on the Nehalem and 1,200 to 13,000 on the Siletz.